Converters Extend Network Analyzer Range As High As 325 GHz
By Yassen Mikhailov, Product Manager, Network Analyzers, Rohde & Schwarz

While the bulk of “mainstream” microwave applications operate below about 6 GHz, many others operate much higher – to 300 GHz and beyond. Most have traditionally been defense related, such as electronic warfare and electronic countermeasures systems, but commercial applications are appearing as well, including adaptive cruise control and future incarnations of WiFi and other personal area networks. These systems and their constituent components must be measured and characterized much as their lower-frequency counterparts, but are well above the measurement frequency range of “core” microwave instruments, of which the vector network analyzer (VNA) is a prime example. Converters have long been available from third parties to extend the measurement frequency of these instruments, but Rohde & Schwarz has developed a family of converters for their four four-port VNAs that cover 75 to 110 GHz and 220 to 325 GHz that deliver significant benefits over these products. The converters can be used with two-port VNAs by adding an external generator.

The company’s four-port VNAs include the R&S ZVA24, R&S ZVA40, and R&S ZVA50, which as their designations indicate have maximum measurement frequencies of 24, 40, and 50 GHz respectively. The R&S ZVA50 was the first VNA to operate up to 50 GHz with up to four ports (see “VNA Extends Four-Port Measurements to 50 GHz”, p. 48). Four-port VNAs make multiport device characterization easier and more accurate because they eliminate the need to connect and reconnect a device to test all its ports.

To 110 GHz….and Beyond
For many years, the performance of external frequency converters employed to extend the measurement frequency range of VNAs remained largely the same. They have been manufactured by third parties and offered as options by instrument manufacturers. In order to more fully exploit the performance of its instruments at these higher frequencies, Rohde & Schwarz has created its own converters.

The R&S ZVA-Z325 converts the input signal of any of the VNAs from 12.22 to 18.06 GHz to an output between 220 and 325 GHz via a WR3.4/WR03 waveguide flange. Its output power at the test port is up to -15 dBm (assuming +9 dBm input power) with accuracy of greater than 4 dB. The output signal can be adjusted using the converter’s variable attenuator by up to 25 dB, which is a significant advantage when characterizing low-noise amplifiers that would otherwise be overloaded. The reference and measurement outputs are up to -13 dBm and are connected via 3.5-mm female interfaces. Dynamic range at a 10 MHz measurement bandwidth is 45 dB, directivity is greater than 30 dB, and trace stability is less than 0.8 dB and 08 deg.

The R&S ZVA-Z110 extends VNA measurement range to 75 to 110 GHz with dynamic range greater than 95 dB (typically 110 dB), which is up to 30 dB higher than other converter solutions. This makes it well suited for evaluating devices such as high-blocking filters, and increases measurement speed since broader bandwidths can be used. RF output power at the test port can be varied by up to 25 dB. Directivity with error correction is greater than 35 dB, and trace stability is +/-2 dB. The converter delivers RF output power of +2 dBm, which the attenuator can reduce to -23 dBm.

If the converters are used with the R&S ZVT20 six-port VNA, a test setup can be configured with up to four converters without an external generator. Setups with up to six converters require an external signal generator for the local oscillators (LOs), with a corresponding high-power LO distribution network. The six-port R&S ZVT20 and converters can also be used to make measurements on frequency-converting waveguide devices. The RF stimulus signals for waveguide test ports 1 and 3 are delivered by different oscillators of the VNA, which makes it possible to apply the stimulus signals to the waveguide test ports with a frequency offset.

The R&S ZVA-Z110 R&S ZVA-Z325 converters were designed to be as small and light as possible in order to conserve space on the test bench, and they are configured to allow easier access to the screw-connected flange joints. The fans traditionally used to cool millimeter-wave converters are not needed, since a passive cooling scheme provides the required heat dissipation. The result is silent operation and operability in particle-sensitive environments such as clean rooms. Optional firmware for the VNAs allows the converters to be fully configured and controlled by the instruments, with diagrams on the display that guide the user through the set-up process. The firmware allows the user to select the measurement set-up, automatically configures the generators to provide the desired RF and LO power and all frequency conversion ratios, selects the test port type and calibration kit, and determines X-axis scaling. The converters can be operated with the company’s “Pulse Profile” option as well, so both the R&S ZVA Series and R&S ZVT20 can be used to make pulsed measurements up to 325 GHz on four-port devices.

RF power delivered to the converter is automatically limited to keep it from being overdriven. Integration with the instrument also increases measurement speed, since no external controllers are required to operate the converter. When the converter is used with a waveguide power sensor, calibration of the analyzer’s reference and measurement receiver power can be performed using its internal receivers, which provides greater dynamic range than when using an RF power meter. The converter comes with two exchangeable test port adapters that accommodate many waveguide sizes, a DC power supply, and two IF cables. The firmware that allows the converter to be integrated into the VNA’s operational structure is optional, as are calibration kits. More information about the converters is available at www.rohde-schwarz.com.

ROHDE & SCHWARZ
www.rohde-schwarz.com
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